There are a few, but the one that always comes to my mind first is in "Timeless", where Harry figures it out in the nick of time and saves the day - having just been berated at by the EMH. The follow-up scene with Janeway is pretty awesome as well, but Harry's "YESS!!!!!!!!!!!!!!" at the last split second was pretty frickin' cool.
Here's the Kim/Janeway bit:

Here's the Kim/Janeway bit: